The present invention relates to a process for the controlled radical polymerization or copolymerization of (meth)acrylic and/or vinyl (for example vinylaromatic) monomers and to the polymers or copolymers thus obtained.
Radical polymerization is industrially one of the most widely used polymerization processes because of the variety of the monomers which can be polymerized, because of the ease of implementation and because of the synthetic processes used (emulsion, suspension, bulk or solution). However, it is difficult in conventional radical polymerization to control the size of the polymer chains and the distribution of the molecular masses. The polymers thus prepared contain chains of very high and very low masses (broad polydispersity), which results in materials with uncontrolled properties. Moreover, the sequential addition of monomer results in a mixture of homopolymers.
Anionic and cationic polymerization techniques, for their part, make possible correct control of the process, but the reaction conditions which these polymerization methods require are not always realizable on an industrial scale. Moreover, many monomers cannot be polymerized by these techniques.
Although there currently exist a few examples of controlled radical polymerization of (meth)acrylic or vinylaromatic monomers, using in particular CuCl/2,2'-bipyridine and RuCl.sub.2 (PPh.sub.3).sub.3 (P=phosphorus and Ph=phenyl) complexes, these catalytic systems have only proved to be active in polymerization at temperatures greater than 100.degree. C., in the absence of activators. Now, when the temperature is high, thermal self-initiation takes place, which results in particular in a decrease in the control of the polymerization.
In addition, for emulsion or suspension polymerization, it is known that the majority of the processes are implemented in aqueous medium and, thus, it is necessary to operate at temperatures of less than 100.degree. C. in order to ensure the stability of these emulsions or suspensions.
The temperature can, certainly, be lowered, but the presence of Lewis acids is then necessary and this involves operating in an anhydrous medium.
It is also necessary for the catalyst not to be degraded by water under normal polymerization conditions. For better control of the polymerization, it is, in addition, preferable to operate in a homogeneous medium (that is to say, with a catalyst which remains soluble in the organic medium).